1. Field of the Invention
The invention relates generally to rotor bearings, and more particularly to systems and methods for preventing rotor bearings from rotating within a stator, where it is not necessary to precisely align the bearings for installation in the stator.
2. Related Art
Oil and natural gas are often produced by drilling wells into oil reservoirs and then pumping the oil and gas out of the reservoirs through the wells. If there is insufficient pressure in the well to force these fluids out of the well, it may be necessary to use an artificial lift system in order to extract the fluids from the reservoirs. A typical artificial lift system employs an electric submersible pump which is positioned in a producing zone of the well to pump the fluids out of the well.
An electric submersible pump system includes a pump and a motor which is coupled to the pump and drives the pump. The electric submersible pump system may also include seals, gauge packages and other components. Because they are designed to fit within the borehole of a well, electric submersible pump systems are typically less than ten inches wide, but may be tens of meters long. The motor of an electric submersible pump system may produce hundreds of horsepower.
The motor of the electric submersible pump system is typically an AC induction motor. The motor has a stator that is cylindrical with a coaxial bore. A rotor (or more than one rotor) is coaxially positioned within the bore of the stator. The rotor is coupled to a shaft so that rotation of the rotor turns the shaft. Bearings hold the shaft, hence the rotor, in position within the bore of the stator and allow the shaft and rotor to rotate smoothly within the bore.
Conventionally, each bearing is held in position within the stator bore by one or more T-rings. The T-rings are seated in a nesting groove around the periphery (the cylindrical outer surface) of the bearing. The T-rings extend radially outward from the bearing and contact the inner diameter of the stator bore. The T-rings thereby provide an interference fit between the bearing and the stator which serves to prevent the bearings from rotating in the stator bore, while also allowing the bearings to move axially within the stator bore to account for thermal expansion of the rotor stack. Such rotation of the bearings will cause unnecessary wear and/or damage to the bearings or the stator, which may lead to rapid motor failure.
There are, however, some disadvantages to using T-rings to hold the bearings within the stator. T-rings are commonly made from an elastomeric material such as EPDM, or ethylene propylene diene monomer. These types of elastomeric materials may not be able to withstand the high temperatures that are experienced by motors in downhole environments. In particular, in SAGD (steam assist, gravity drain) applications that are used to get oil out of tar sands, the downhole temperatures typically exceed 200 C. At these temperatures, EPDM loses its mechanical integrity and fails, so that the T-rings are no longer capable of properly securing the bearings and preventing them from rotating within the stator bore.
It would therefore be desirable to provide a mechanism for securing the bearings, and particularly for preventing the bearings from rotating in the stator bore while allowing axial bearing movement to account for thermal expansion, where the new mechanism does not fail in the high temperatures of downhole environments.